US President Donald Trump says he has authorised the doubling of steel and aluminium tariffs "with respect to Turkey".
Mr Trump said in a tweet that the tariff on aluminium imports will be increased to 20% and the tariff on steel imports will be raised to 50% as the Turkish lira "slides rapidly downward against our very strong Dollar!".
Mr Trump is also declaring that "Our relations with Turkey are not good at this time!".
I have just authorized a doubling of Tariffs on Steel and Aluminum with respect to Turkey as their currency, the Turkish Lira, slides rapidly downward against our very strong Dollar! Aluminum will now be 20% and Steel 50%. Our relations with Turkey are not good at this time!— Donald J. Trump (@realDonaldTrump) August 10, 2018
The United States imposed sanctions on two Turkish officials earlier this month over a detained American pastor who is being tried on espionage and terror-related charges.
Turkey vowed retaliation "without delay" and warned the move would further harm relations between the two allies.
Mr Trump's tweet caused a further drop in the Turkish currency, which is now down 13% on the day.
Turkish President Recep Tayyip Erdogan has appealed for calm as the currency plunges, urging people to change foreign money into local lira.
This is what happened to the lira as Turkey's President Recep Tayyip Erdogan urged his fellow countrymen to sell gold, euros and dollars in exchange for the lira. pic.twitter.com/ae0px3AhGd— Financial Times (@FinancialTimes) August 10, 2018
Mr Erdogan said during an address to supporters: "Change the euros, the dollars and the gold that you are keeping beneath your pillows into lira at our banks. This is a domestic and national struggle."
He appeared to blame foreigners for trying to hurt Turkey, saying: "This will be my people's response against those waging an economic war against us."
Mr Erdogan reportedly said his government "will not lose the economic war".
Turkish newspaper Hurriyet and other media reports quote Mr Erdogan as making the comment to a group of worshippers following traditional Muslim Friday prayers during a visit to the northern city of Bayburt.